The present invention is directed to a blast joint, particularly, a blast joint comprising a series of blast joint modules connected to form a blast joint having a length exceeding the standard length of production tubing for use in production zones of substantial thickness.
It is common when drilling oil and gas wells to encounter two or more producing formations or zones. In such a situation, each producing formation is produced through a separate string of production tubing extending into the well bore. Typically, a string of production tubing extends to the lowermost producing formation. A packer is set about the production tubing string between the producing formations to isolate the upper producing formation from the lower producing formation. A second string of production tubing extends into the well bore to the upper producing formation. A packer is set above the upper producing formation to close off the annulus about the two strings of production tubing so that the upper production zone is isolated between the two packers. Thus, each string of production tubing is in fluid communication with the producing formation adjacent the lower open end of the production tubing. This is commonly referred to as a dual completion well.
Downhole well equipment is exposed to erosive elements in the well bore. This is particulaly true in a dual completion well where one string of production tubing extends through an upper producing zone. Flow into the well bore in the upper producing zone, particularly in formations producing high pressure gas, is at high velocities. Abrasive materials, such as unconsolidated sand grains, are often entrained in the fluid stream and impinge on the production tubing. This action is extremely abrasive and erodes the pipe surface, thus requiring replacement of the production tubing. This is a very time consuming process which may be repeated often, particularly for wells having high sand content.
The erosiveness of producing fluids is well known in the prior art and many different efforts have been made to solve the problem. U.S. Pat. No. 4,381,821 discloses a series of elements composed of an abrasion resistant material mounted about a tubular member. The elements form a protection ring about the tubing and are supported on the tubular member by upper and lower supports which provide tongue and groove engagement with the upper end of an upper ring and with the lower end of a lower ring.
U.S. Pat. No. 3,379,259 discloses a system for protecting the production tubing comprising a plurality of baffle sleeves concentrically mounted about the production tubing in the area of an upper producing formation. Each of the sleeves includes perforations which are staggered in relations to perforations in the next adjacent sleeve so that the erosive fluid entering the well is forced to follow a tortious flow path before it impinges on the production tubing. The changing flow path causes the erosive fluid to decrease its kinetic energy and reduce its impact velocity before it reaches the production tubing, thereby reducing erosion of the tubing.
U.S. Pat. Nos. 4,141,368 and 4,028,796 to Bergstrom disclose a blast joint comprising a series of short cylindrical rings composes of cemented tungsten carbide and the method of producing a blast joint for oil well production tubing. The rings are disposed coaxially in contact with each other between end retaining rings mounted upon a supporting steal tube which comprises a single section or joined sections of production tubing.
In U.S. Pat. No. 4,211,440, Bergstrom suggests that the successful functioning of the blast joint in a well is dependent upon the handling of the blast joint before it is positioned in the well. To this end, Bergstrom discloses the introduction of a yieldable compression spring encircling the production tubing and disposed between the end of the carbide rings and the ring retaining clamp to allow freedom of movement of the rings relative to the tubing to permit handling and moving of the assembled blast joint without damage to the carbide rings.
The use of blast joints as protective structures for protecting production tubing is well recognized in the prior art. However, blast joints of the prior art are typically limited to providing protection of a single joint of production tubing. If a blast joint of an extended length is required, a series of tubing joints or pipe joined by a flush joint are used to form the blast joint. The prior art method of forming blast joints having flush joint connections is exemplified by U.S. Pat. No. 4,028,796 to Bergstrom. Flush joints, however, substantially reduce the tensile strength of the production tubing string at the flush joint connection. The blast joint of the present disclosure overcomes the disadvantages of flush joint connections by providing a shielded connection assembly for joining the threaded pin end of a tubular member to the threaded box end of a tubular member connected therewith to form the blast joint.